commit a27a0c9b6a208722016c8ec5ad31ec96082b91ec upstream.

It turns out that the current version of gfs2_metadata_walker suffers
from multiple problems that can cause gfs2_hole_size to report an
incorrect size.  This will confuse fiemap as well as lseek with the
SEEK_DATA flag.

Fix that by changing gfs2_hole_walker to compute the metapath to the
first data block after the hole (if any), and compute the hole size
based on that.

Fixes xfstest generic/490.
Signed-off-by: NAndreas Gruenbacher <agruenba@redhat.com>
Reviewed-by: NBob Peterson <rpeterso@redhat.com>
Cc: stable@vger.kernel.org # v4.18+
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>